Urban Wastewater Treatment by Infiltration Percolation: Comparative Study of the Purification Performance of Sand Filter Through a Simple and Double Column

The objective of this work is to study the effectiveness of the infiltration–percolation process on sand, as a complementary treatment of a secondary effluent, to improve the physicochemical and bacteriological quality of the treated wastewater from the purification station of Zarat. A comparative study was undertaken to evaluate the effect of the double filtration (50 cm) on pollutant removal efficiencies, compared to the simple filtration (1 m). Experiments evaluate the purifying power of the double filtration. Indeed, our results show that at the level of the first 50 cm, most of the COD is removed and about 70% of the organic nitrogen and ammonium have been oxidized in a sand filter. The elimination of microorganisms has been observed largely in the superficial layers. This leads us to deduce that a filtration of 50 cm of sand is sufficient for the filtrate to be discharged into the sea with reduced nitrate content and a minimum residence time, while the reuse of wastewater in agriculture requires filtration over a greater thickness of sand to remove most pollutants that can cause health risks and affect plants. This is explained by the increase in purification performance after double filtration in terms of COD, with a reduction of 71%, as well as for total nitrogen and ammonia which evolve with a treatment efficiency of 97% and 96%, respectively. The microbiological results showed that the double filtration ensures a better elimination of fecal contamination germs than a simple filtration, thus contributing to a significant improvement of the quality of the purified water of the Zarat wastewater treatment plant.